Process for making radioactive iodine



nited States Patent Illinois No Drawing. Filed Mar. 12, 1959, Ser. No.798,808 6 Claims. (Cl. 23-218) This invention relates to a method ofproducing radioactive iodine in particular, it relates to a method ofproducing said radioactive iodine by neutron bombardment ofmeta-telluric acid.

Radioactive iodine hereinafter referred to as 1 is an important tool inthe hands of the clinician. Among its many uses may be mentioned its useas an index of basal metabolism and treatment of thyroid tumors. I isadministered to the subject intravenously and is collected by thethyroid gland in accordance with the particular affinity of that organfor iodine. Activity of the thyroid gland is' an index of basalmetabolism. Such activity can be measured in terms of the amount ofiodine which is attracted thereto. The tracer properties of radioactiveiodine provide an evaluation of the degree of attraction to the thyroidgland by employing Well-known methods of radioactive counting. This particular relationship of the thyroid and iodine also explains themechanism whereby thyroid tumors can be treated by radioactive emissionsafter I has been deposited in the thyroid gland. Other adaptablepractices of I are knownor are actively being investigated.

The prior art provides two methods for producing 1 both of which arecharacterized by serious disadvantages. One method provides productionof I as a fission byproduct following neutron bombardment of uranium ina reactor. This uranium by-product process results in a 2% to 3% fissionyield of I but the actual chemical yield is low due to processing andaging. The other wellknown method employs metallic tellurium ortellurium oxide to produce I The tellurium metal is a target material ina neutron flux reactor, and after a suitable period of irradiation,metallic tellurium, which is 35.4% tellurium is converted to theradioactive isotope tellurium This latter material is spontaneouslyconverted to I following fi-emission. While this method results in ahigher recoverable yield than the fission byproduct method, it isactually less desirable. This is attributed to the complex and difficultseparation steps necessary to obtain I from the irradiated targetmaterial.

Ortho-telluric acid has recently been described as a target material for1 production (R. Constant, J. Inorg. Nucl. Chem, 1958, vol. 7, pp.133-139). This particular target provides fairly easy separation, butthis particular acid has the disadvantages of low-temperature stability,small tellurium content and low specific density.

It is an object of this invention to provide amore efiicient method forthe production of I Another object of this invention is to provide amethod whereby the production of I is characterized by higher yields.

A still further object of this invention is to provide a method of 1production Which is complemented by a simple separation procedure.

In the accomplishment of the foregoing objects and other objects whichwill be apparent hereinafter, it is now provided that meta-telluric acidcomprises the target material in a high-flux neutron reactor.Meta-telluric acid, H TeO has a density of 3.50 and a tellurium contentof 66%. Meta-telluric acid is unstable above the elevated temperature of160 C. By the term unstable is meant the loss of a mole of Water from amole of metatelluric acid after the temperature of stability has beenexceeded. This temperature of stability for meta-telluric fied period oftime.

3,033,652 Ice Patented May 8, 1962 acid is high and comprises a decidedadvantage over ortho-telluric acid as will be more fully disclosed in alater portion.

The improved method substantially provides deposition of the targetmaterial in a capsule or equivalent container made of aluminum or othersuitable materials. The term target material will be employed herein asa synonym for meta-telluric acid. The capsule is placed in a high-flux,low-temperature (less than C.) reactor which may be air-cooled such asthe Brookhaven reactor or water-cooled such as a heterogenouswatercooled medium testing reactor (MTR) type. A definite neutron fiuxis directed at the target material for a speci- The neutron flux isexpressed as the number of neutrons traversing a square centimeter ofspace per second (n./cm. /sec.). The method is successfully operated atvarying neutron flux, but it is desirable to employ higher flux in orderto obtain more I activity per gram of target material. The quantityconcept relates to the radioactivity of I in units of curies (c.) ormillicuries (me). The curie is defined as the quantity of anyradioactive nuclide in which the number of disintegrations per second is3.700X10 The radioactive activity of I obtained by this method may beapproximately calculated from the formula:

Flux Approximate Saturation Yield 10 nJcmfi/see 10 n.,"cm. /sec 10n./cn1.'-/sec 10 nJcmfi/scc 1.0 mc./gm.Te-.

10.0 me./gm.Te.

100.0 mc./gm.Te.

1,000.0 mc./gm.Te or 1 curie.

After meta-telluric acid has been exposed to the prescribed irradiationconditions, 1 is easily separated therefrom by dissolving the targetmaterial in distilled water and adding thereto a strong mineral acidsuch as sulfuric, phosphoric and the like.

A preferred practice provides the addition of a carrier to the solution.A carrier such as potassium iodide is added in an amount of 50-100micrograms. This amount of stable iodide is suflicient to act as acarrier for the radioactive 1 atoms formed in the process.

The solution is distilled and the formed iodine can be converted fromthe ionic state to the molecular state or I- to I It is also provided inalternative practice that the iodine ions are passed into a containerwith a solution of sodium sulfite, thereby obtaining I in the sodiumiodide form. This separation procedure is obtained with facility becausethe target material is soluble in water and is a mild oxidizing agent.

In the practice of this process, it is provided that a high-flux,low-temperature reactor can be utilized, thus, providing a higherneutron flux Without incurring difiiculties from the development ofexcessively high temperatures. The presence of high temperatures beyondthe workable limits of the process would result in decomposition ofmeta-telluric acid or undesirable vaporization pressures arising fromliberated water. This is a limiting disadvantage for a capsule or acontainer of a given volume. As described hereinbefore, meta-telluricacid is unstable at temperatures in excess of 160 C. Such excessivetemperatures should result in liberation of water in meta-telluric acidin vapor form. The build-up of vapor pressure would result in rupturingthe capsule containing the target material. This is an occurrence whichobviously should be avoided and it is very difficult to avoid withortho-tellurium acid which has a low-temperature stability of 90 C. Itis, therefore, apparent that the high-temperature stability ofmeta-telluric acid comprises an advantage in the use of this targetmaterial. Cooling the reactor with water will allow use of a highfluxrate and control of temperature conditions at a level below thedecomposition temperature. Such desirable high-flux rates can beattempted in a low-temperature, high-flux, air-cooled reactor Withoutleading to temperatures which would decompose the target material.

The process is practiced to advantage over orthotelluric acid becausemeta-telluric acid has a higher tellurium content which amounts to 66%.This allows a large amount of tellurium in a given capsule. The use ofmeta-telluric acid is also superior to ortho-telluric acid becausemeta-telluric acid has a higher density of 3.50. This provides a goodamount of tellurium target in a relatively small target volume. Suchfeatures provide economical advantages for neutron bombardment in areactor.

Embodiments of the process are presented in the following illustrations,but it is intended that such illustrations be considered only as ateaching rather than an exclusive practice.

Example I An aluminum capsule measuring one inch in diameter and threeinches in length is filled with 100 gms. of meta-telluric acid. Thecapsule is placed in a watercooled reactor of the MTR type aifordingn./cm. sec. The temperature of the target material is maintained below160 C. The irradiation period is continued for 16 days. The targetmaterial is transferred from the aluminum capsule to a mixturecomprising 1500 ml. of distilled water, 100 ml. of concentrated sulfuricacid and 100 micrograms of potassium iodide. The mixture is present inan enclosed flask to which is attached distilling apparatus. Thesolution is distilled under application of heat. The distillate iscollected in a receiver containing 10 ml. of Na SO solution.Distillation is continued until a volume of 20 ml. has been collected.This is a recoverable yield of 36-40 curies I131 The distillation stepsare not characterized by any critical features. Conventional procedureswell known in the art of distillations are operable. It is desirable toperform the distillation in an acid medium to obtain the best results;any strong mineral acid which is non-volatile and is not carried away bythe steam distillate is useful. Various aqueous-acid mixtures may beemployed, but the preferred mixture comprises about a 6% solution ofacid in water.

Example 11 In an aluminum capsule is placed 1.52 gms. of metatelluricacid and the capsule with target is irradiated at 1.65 1O n./cm. /sec.for 11.7 days in the north face of the Brookhaven reactor (air-cooled),

The target material is transferred to a distilling flask containing 15m1. of 1 N H 50 plus 100 micrograms of potassium iodide carrier. Themixture is warmed until the target dissolves and is then distilled witha nitrogen purge. The distillate is collected to a volume of 3 ml. in atrap containing 3 ml. of Na SO solution (2 mg./ ml.)

The obtained yield is me. I at pile-out time. EX- amining the bottoms ofthe distilling apparatus shows that no emissions due to 1 occur. Thisindicates the recovery is quantitative.

I claim:

1. A method for making radioactive iodine which comprises irradiatingmeta-telluric acid with a neutron flux in a high flux, low temperaturereactor, irradiating said meta-telluric acid at a reactor temperaturenot in excess of 160 C., and separating iodine from the irradiatedm'eta-telluric acid.

2. A method for producing radioactive iodine which comprises irradiatingmeta-telluric acid with a neutron fiux in a high-flux, low-temperature,air-cooled reactor, irradiating said meta-telluric acid at a reactortemperature not in excess of 160 C., dissolving the irradiatedmetatelluric acid in water made acidic by a strong, nonvolatile mineralacid and separating I by distillation.

3. A method for producing radioactive iodine which comprises irradiatingmeta-telluric acid with a neutron flux in a water-cooled reactor,irradiating said metatelluric acid at a reactor temperature not inexcess of 160 C., dissolving the irradiated meta-telluric acid in watermade acidic by a strong, non-volatile mineral acid and separating iodineby distillation.

4. A method according to claim 3 where the irradiated meta-telluric acidis dissolved in an aqueous medium containing about 6% of a strong,non-volatile mineral acid.

5. A method for making radioactive iodine which comprises irradiatingabout gms. of meta-telluric acid with a neutron flux of 10 n./cm. /sec.in a watercooled reactor for about 16 days at a reactor temperature notin excess of C., dissolving the irradiated metatelluric acid in about1500 ml. of a water solution containing about 6% concentrated sulfuricacid and separating iodine by distillation.

6. A method for making radioactive iodine which comprises irradiatingabout 1.5 gms. of meta-telluric acid at a neutron flux of about 1.65 10n./cm. /sec. in a high-flux, low-temperature, air-cooled reactor forabout 12 days at a reactor temperature not in excess of 160 C.,dissolving the target material in about 15 ml. of 1 N H 50 addingthereto between 50 and 100 micrograms of a carrier and separating I fromthe carrier by distillation.

References Cited in the file of this patent FOREIGN PATENTS GreatBritain Dec. 19, 1956 OTHER REFERENCES

2. A METHOD FOR PRODUCING RADIOACTIVE IODINE 131 WHICH COMPRISESIRRADIATING METAL-TELLURIC ACID WITH A NEUTRON FLUX IN A HIGH-FLUX,LOW-TEMPERATURE, AIR-COOLED REACTOR, IRRADIATING SAID META-TELLURIC ACIDAT A REACTOR TEMPERATURE NOT IN EXCESS OF 160*C., DISSOLVING THEIRRADIATED METATELLURIC ACID IN WATER MADE ACIDIC BY A STRONG,NONVOLATILE MINERAL ACID AND SEPARATING 1131 BY DISTILLATION.